Working with DEMs in Terragen

There are many programs that will convert DEMs into a format suitable for
Terragen. This page describes how I use 3DEM to
create my terrains from DEMs including joining multiple files together.

Single DEMs

3DEM provides a Terragen export under the file menu but the size of the
terrain is usually smaller than what you can squeeze out of the data.
Instead, I save a BW version of the map image and import it into Terragen via
the Firmament BMP import. To create the BW map in 3DEM requires a few small
modifications.

Lighting Properties

The first modification is to get rid of any shading. This is easily done in
the lighting parameters (Color Scale > Shaded Relief).

This places the sun directly above the terrain resulting in no shadows.

Terrain Colours

The next modification is to change the Terrain Colours (Color Scale >
Modify Scale).

Edit the colours for each step starting from R0, G0, B0, incrementing each
step by 19. Save the file so that it can be reloaded in future (or
borrow mine)

It may be necessary to increase the altitude range to avoid flattening out
the highest points of the terrain.

Multiple DEMs

There is a world wide conspiracy of map makers that results in many places of
interest being mapped to the corners of maps, requiring you to buy 4 maps. The
same seems to apply for DEMs.

Unfortunately 3DEM only displays single DEMs. It is possible with a bit of
work to join multiple DEMs in another image editing program. This is relatively
straightforward if all of the images have the same altitude to pixels value
settings. Firstly, load each section into 3DEM and take a note of the altitude
range displayed in the Terrain Colors dialogue box. Take a note of the minimum
and maximum altitudes of all of the images you want to join, round them to the
nearest 100 metres (round down for minimum, round up for maximum) and use these
to modify the Terrain Colours of each DEM and save each map image.

It's then a relatively straightforward to join process of joining the
sections together, editing any minor glitches that may occur (e.g. small gaps).
In this way it's possible.